So when I pulled my thermostat out of my 2011 mini, with a part manufactured 12 years ago and 72,000 miles, and a leak just at the back of transmission about 6 inches to the left of the Thermostat, I expected to see a visible cracked thermostat or a damaged cross over pipe exit. However, the water pipe on that side was fine (the other side was back to a crackling crunch) but I already have my water pump out so it was easy to get the broken pieces out. Also, I don't see any visible cracks on the Thermostat. So it was only mildly leaking when hot, about a 1/4 cup till cool. Also, not AC condensate. I felt it was coolant and also the expansion tank had to be refilled after every 4th drive of the vehicle.

However, I noticed this pipe on top of the transmission which wasn't connected to anything and the end is flared like it was connected to something. I never disconnected it... Is it possible my coolant is leaking out of this pipe?? I don't know where this is supposed to go?




This can't be the A/C condenser drain or washer fluid drain because it has a flared end like it was connected to something some time.

 

Ok, that looks like a part #, suggesting this: https://www.ecstuning.com/b-genuine-...e/24007563920/
Overflow vent for Transmission.

Ok, never mind, that's not it. I'm going to have to hope my thermostat has a leak and I just can't see it.

 

The thermostat housing can leak only when it's hot and under pressure. I don't know if you will see a crack when it's cooled off to ambient temp. Also could be the o-ring seal/gasket that was leaking. Those get hard and flat over time with heat cycling. If you get it all back together with the new parts and the leak has stopped, then you indeed found and fixed the problem, even if you don't know EXACTLY what it was.